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DUBAI, Dec 4 (Reuters) - The leader of the Islamic State in Iraq, an al Qaeda-linked group forced on the defensive by its former tribal allies, ordered a renewed bombing campaign against Iraqi security forces in a Web message on Tuesday.

"This campaign should be based on explosives and its target should be the apostates ... wearing uniforms and all those who fight alongside the occupiers," Abu Omar al-Baghdadi said in an audio recording posted on an Islamist Web site.

"Every soldier (militant) is to detonate at least three bombs by the end of the campaign," he said.

The campaign would continue until an Islamic date corresponding to the last days of January, he added.

While the Iraq wing of al Qaeda remains at the forefront of many groups fighting U.S. forces and the Shi'ite-led government supported by Washington, its fighters have faced growing opposition in the Sunni areas of Iraq where they operate.

Angered by months of deadly attacks against Iraqis who fail to follow their hardline interpretations of Islam, Sunni tribes have begun to turn against the al Qaeda militants they once backed.

U.S. military and civilian casualties in Iraq have dropped sharply in the past two months, partly as a result of 30,000 additional U.S. troops targeting al Qaeda fighters and Shi'ite Muslim militias. The troops became fully operational in mid-June.

The military says attacks have dropped 55 percent since the troop "surge".

More efficient Iraqi security forces and an increased use of U.S.-backed neighbourhood police units organised by mainly Sunni Arab tribal leaders have also been credited for the decline in violence.

Baghdadi made a similar call in mid-September marking the beginning of Islam's holy month of Ramadan. (Reporting by Inal Ersan; Editing by Michael Winfrey)

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